FIG. 1 is a block diagram of an exemplary wireless backhaul network 100 for a communication system. The wireless backhaul network 100 has a tree topology connecting one or more access points, represented by the “leaf” nodes 120-2, 120-3, 120-5, and 120-6, to a “congregate” node 110, which is in turn connected to a core network of a communication system (not shown). Intermediate between the access points 120-2 and 120-3 and the congregate node 110 is the “relay” node 120-1. Likewise, intermediate between the access points 120-5 and 120-6 and the congregate node 110 is the relay node 120-4. Connecting the nodes 120-i and the congregate node 110 are 6 bidirectional wireless communication links 130-i (i=1, . . . , 6).
Access traffic from surrounding adjacent user devices can be incident at any node 120-i in the backhaul network 100, including the relay nodes 120-1, 120-4. The traffic is bidirectional, and can be divided into “uplink” traffic (to be conveyed from the node 120-i to the congregate node 110) and “downlink” traffic (to be conveyed from the congregate node 110 to the node 120-i). Each bidirectional link, e.g. 130-1, therefore comprises two directional link “components”, an uplink 130u-1 and a downlink 130d-1. The traffic is converted to signals on the links 130-i for conveyance through the network 100. The capacity of the wireless backhaul network 100 for conveying this traffic has a strong impact on the capacity of the communication system of which the wireless backhaul network 100 forms part.
The problem of frequency allocation within a backhaul network is how to allocate spectrum within a predetermined frequency range to each directional link component so that as much as possible of the incident traffic at the nodes served by the link may be conveyed through the network. A complication is that links can interfere with one another, e.g. the uplink and downlink components of a single link, or two link components transmitting to the same node, so the allocation must take this potential for interference into account.
In conventional wireless backhaul networks, manual efforts are used to statistically allocate frequencies “optimally” within the network, and then the statistically “optimal” frequency allocations are fixed for months or years. However, the performance of such manual frequency allocation for general tree-structured multiple-hop wireless backhaul networks is extremely low. Hence, to improve access data rates in multi-user communication systems employing backhaul networks, more efficient techniques for frequency allocation are desirable.